Abstract:
In this talk, I will discuss the asymptotic behavior of
solutions of one-dimensional semilinear diffusion
equation of the form
u_t = u_{xx} + f(x,u)
on the whole line, where f is a smooth function satisfying
f(x,0) = 0, f(x,u) = f(x+L,u) for some L > 0.

We consider the behavior of general solutions whose
intial data are either of the Heaviside function type or
compactly supported.

Under rather a mild additional assumption on f, we
show that the solution approaches, as t tends to infinity,
what we call a “propagating terrace”, which roughly means
a layer of pulsating traveling waves with different speeds.

In the special case where the nonlinearity f is monostable,
bistable or of the combustion type, the propagating terrace
is nothing but a single pulsating traveling front.
Our results answers many open questions concerning
the spreading fronts in periodic environments.